Method of recovery of zinc and other metals from metallurgical fines

ABSTRACT

A method and recovering method of recovering zinc oxides and other metal oxides having an injection chamber where a mixture of natural gas and oxygen is formed and then ignited to form high temperature combustion gases of greater than 2000° C. with a high concentration of carbon monoxide. Then, the mixture is transported through a quiescent chamber to a feed chamber where the ignited high temperature combustion gases are mixed with finely divided material, including EAF dust. The mixture is transported to a reaction chamber, wherein zinc vapor and other metal vapors and molten slag particles are formed. The zinc vapor and other metal vapors are separated from the molten slag particles and transported to an insulated plenum. Zinc vapor and other metal vapors are mixed with air and become airborne zinc oxide and other metal oxides. The airborne zinc oxide and other metal oxides are collected.

This non-provisional application claims priority to U.S. Provisional Application No. 62/488,750, filed on Apr. 22, 2017, and is incorporated herein by reference in its entirety.

BACKGROUND AND SUMMARY OF INVENTION

Pyrometallurgical treatment of finely divided ores, concentrates, slags and other materials to recover zinc and other metals is well developed. Examples of technologies involving said treatment may be found in U.S. Pat. Nos. 4,654,077 and 4,732,368. Previous methods and apparatus for pyrometallurgical treatment used a combustion chamber extending through two or more coaxially positioned chambers. Combustion gases were ignited and expanded in a first coaxially positioned chamber. Then, the combustion gases were expanded again and mixed with finely divided ore, concentrate, slag, or other material as said combustion gases enter a second coaxially positioned chamber. Coal or a similar solid material was used as fuel with the addition of oxygen, to produce carbon monoxide gas as the primary reducing agent, at a temperature well above the boiling point of the elemental metal (e.g. well above 907° C. for zinc).

With the introduction of natural gas fired rich-burning combustors, for example as described in U.S. Pat. No. 5,427,524, there has been an effort to further develop natural gas fired systems. Methods and apparatus for creating a combustor capable of producing hot combustion gases and a stable flame useful in combustion processes may be especially beneficial in the pyrometallurgical treatment of finely divided ores, concentrates, slags and other materials. Prior combustors form relatively low luminous flame under fuel rich conditions (i.e. oxygen to fuel ratios that are less than stoichiometric). These natural gas fired rich-burning combustors have been used to recover zinc and lead from electric arc furnace (EAF) dust and other experimental recovery of zinc from sludge and filter cake from waste and water treatment facilities associated with metal electroplating operations.

However, these prior processes have had serious problems with leaks. Leaks may be caused by breakdown of welds and water leaks in the equipment in which the system is performed. These leaks require the dismantling of the system and repairing of the injection chamber, feed chamber, and/or reactor chamber. Furthermore, leaks in the slag separation chamber may also require shutdown of the process, followed by clean out and repair of the slag separation. Additionally, slag particles can buildup in the reaction chamber and the plenum, requiring shutdown to clean and repair this equipment. Therefore, there is a need to improve the processes to provide a more efficient and safer method for recovery of zinc and other metals from metallurgical fines, e.g. EAF dust.

Disclosed here is a method of recovering zinc oxide and other metal oxides from metallurgical fines, comprising:

-   -   a. forming in an injection chamber a mixture of natural gas and         oxygen and then igniting the mixture to form high temperature         combustion gases of greater than 2000° C. with a high         concentration of carbon monoxide;     -   b. transporting the ignited high temperature combustion gases         through a quiescent chamber surrounded by a cooling jacket and         located below the injection chamber;     -   c. transporting the ignited high temperature combustion gases         from the quiescent chamber to a feed chamber surrounded by a         cooling jacket and located below the quiescent chamber;     -   d. forming in the feed chamber a mixture of the ignited high         temperature combustion gases with injected finely divided         material including EAF dust;     -   e. transporting the mixture of the ignited high temperature         combustion gases with injected finely divided material including         EAF dust to a reaction chamber surrounded by a cooling jacket,         wherein carbon monoxide in the ignited high temperature         combustion gases react with metal compounds in the finely         divided material forming zinc vapor and other metal vapors and         molten slag particles;     -   f. transporting said the mixture, including the zinc vapor and         other metal vapors and slag particles, from the reaction chamber         through a transition piece to a slag separation chamber         surrounded by a cooling jacket and located tangentially to the         reaction chamber, wherein the zinc vapor and other metal vapors         are separated from the molten slag particles;     -   g. transporting the zinc vapor and other metal vapors to an         insulated plenum, wherein the zinc vapor and other metal vapors         are mixed with air and become airborne zinc oxide and other         metal oxides; and     -   h. transporting the airborne zinc oxide and other metal oxides         from the insulated plenum to a filter baghouse where zinc and         other metal oxides are collected and the remaining gases are         released to the atmosphere.

This method provides for separate injection and control of oxygen and natural gas in the injection chamber, initially concentrically through the injection chamber and then mixing the oxygen and natural gas by turbulent flow in the lower part of the injection chamber and into the reaction chamber as desired. Additional oxygen and natural gas may also be injected later, in the injection chamber and in the feed chamber, to provide a desired mixture of oxygen and natural gas through the reaction chamber. In some embodiments, the method may have components made of high heat conduction material, such as copper, in the injection chamber, quiescent chamber and/or feed chamber in contact with natural gas and oxygen reaction products for reliable and effective cooling of the apparatus to provide more effective operation of method.

The quiescent chamber is located below the injection chamber. The quiescent chamber may be provided as an extension of the injection chamber, an introduction to the feed chamber, or as a separate chamber.

In some embodiments, a tap may be provided in the slag separation chamber to continuously or intermittently remove collected slag from the slag separation chamber. In these embodiments, a permanent or temporary heating unit may be provided adjacent to the slag separation chamber to maintain slag fluidity and to prevent air from entering the slag separation chamber.

Also disclosed is an apparatus for recovering zinc oxide and other metal oxides, comprising:

-   -   a. an injection chamber, where natural gas and oxygen are mixed         and then ignited to form high temperature combustion gases of         greater than 2000° C. with a high concentration of carbon         monoxide;     -   b. a quiescent chamber surrounded by a cooling jacket, where the         ignited high temperature combustion gases are transported to;     -   c. a feed chamber surrounded by a cooling jacket, where the         ignited high temperature combustion gases are mixed with finely         divided material including EAF dust;     -   d. a reaction chamber surrounded by a cooling jacket, where         carbon monoxide in the ignited high temperature combustion gases         react with metal compounds in the finely divided material         forming zinc vapor and other metal vapors and molten slag         particles;     -   e. a slag separation chamber surrounded by a cooling jacket and         tangentially to the reaction chamber, where the zinc vapor and         other metal vapors are separated from molten slag particles;     -   f. an insulated plenum, where the zinc vapor and other metal         vapors are mixed with air and become airborne zinc oxide and         other metal oxides; and     -   g. a filter baghouse, where the zinc oxide and other metal         oxides are collected and remaining gases are released to the         atmosphere.

In some embodiments, the apparatus may have components, such as the injection chamber, quiescent chamber, feed chamber, reaction chamber and slag separation chamber, made of high heat conduction material, such as copper, providing effective cooling of the apparatus.

The apparatus may further comprise a tap provided in the slag separation chamber. The tap provides continuous or intermittent removal of collected slag. Additionally, a heating unit may be provided adjacent to the slag separation chamber to maintain slag fluidity and to prevent air from entering the slag separation chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

In addition to the features mentioned above, other aspects of the present invention will be readily apparent from the following descriptions of the drawings and exemplary embodiments, wherein like reference numerals across the several views refer to identical or equivalent features, and wherein:

FIG. 1 is a flowchart illustrating a method of recovering zinc oxide and other metal oxides in accordance with an aspect of the innovation;

FIG. 2 is an illustration of the innovation is described;

FIG. 3 is an enlarged fragmentary view of the injection chamber, quiescent chamber, and feed chamber equipment shown in FIG. 2;

FIG. 4 is an enlarged fragmentary view of the injection chamber, quiescent chamber, feed chamber, reaction chamber and slag separation chamber equipment shown in FIG. 2;

FIG. 5 is as a side view of FIG. 4;

FIG. 6 top view of the slag separation chamber of FIG. 2;

FIG. 7 is a partial end view of the slag separation chamber shown in FIG. 6;

FIG. 8 is an enlarged side view of the slag separation chamber shown in FIG. 6;

FIG. 9 is an enlarged fragmentary view of the tap region of slag separation chamber.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a method of recovering zinc oxides and other metal oxides is described. At 100, in an injection chamber, a mixture of natural gas and oxygen is formed and then ignited to form high temperature combustion gases of greater than 2000° C. with a high concentration of carbon monoxide. At 110, the ignited high temperature combustion gases are transported from the injection chamber through a quiescent chamber, which is surrounded by a cooling jacket. At 120, the ignited high temperature combustion gases are transported from the quiescent chamber to a feed chamber where the ignited high temperature combustion gases are mixed with finely divided material, including EAF dust. The feed chamber is surrounded by cooling jacket. At 130, the mixture of ignited high temperature combustion gases with injected finely divided material is transported to a reaction chamber, which is surrounded by a cooling jacket, wherein the carbon monoxide in the ignited high temperature combustion gases react with metal compounds in the finely divided material forming zinc vapor and other metal vapors and molten slag particles. At 140, the mixture, including the zinc vapor and other metal vapors and slag particles, is transported from the reaction chamber through a transition piece to a slag separation chamber surrounded by a cooling jacket. The slag separation chamber is located tangentially to the reaction chamber. In the slag separation chamber, the zinc vapor and other metal vapors are separated from the molten slag particles. At 150, the zinc vapor and other metal vapors are transported to an insulated plenum. In the plenum, the zinc vapor and other metal vapors are mixed with air and become airborne zinc oxide and other metal oxides. At 160, the airborne zinc oxide and other metal oxides are transported from the insulated plenum to a filter baghouse where zinc and other metal oxides are collected and the remaining gases are released to the atmosphere.

FIGS. 2 to 9 illustrate an apparatus to perform the present method of recovering zinc oxides and other metal oxides. A method of recovering zinc oxides and other metal oxides is shown comprising an injection chamber 10, quiescent chamber 20 below injection chamber 10, a feed chamber 30 below the quiescent chamber 20, a reaction chamber 40 below the feed chamber 30, then transition to a slag separation chamber 50 where slag is removed, a plenum chamber 60 where zinc oxide and other metal oxides are moved in airborne particulate and a bag house 70 where zinc oxide and metal oxides are collected and other gases exhausted off.

Specifically referring to FIGS. 2 and 3, the injection chamber 10 is shown with oxygen inlets 11 and natural gas inlet 12 from where oxygen and natural gas are transmitted coaxially through the injection chamber 10. Baffling 13 is provided to enable the initial oxygen and natural gas to flow separately coaxially through the injection chamber 10. In the lower part of injection chamber 10, oxygen and natural gas are mixed by turbulent flow. The injection chamber 10 also has an ignitor 14 that provides for ignition of the substoichiometric mixture of natural gas and oxygen to form a combustion gas enriched with carbon monoxide.

Below the injection chamber 10, quiescent chamber 20 enables the oxygen and natural gas to thoroughly mix before reaching feed chamber 30. The quiescent chamber 20 also provides for the finely divided material from the feed chamber 30 not to freeze onto the walls of the chambers. The finely divided material freezing onto the walls of the chambers may inhibit mixing. Therefore, the quiescent chamber provides for the increase of process efficiency. The quiescent chamber 20 may be a separate chamber as shown or as upper part of the feed chamber 30 or as lower part of the injection chamber 10. In any case, the quiescent chamber 20 is surrounded by a cooling jacket 22, typically of eighth inch or quarter inch passageways, through which water is circulated to cool the walls of the chamber (typically of metal).

Following the quiescent chamber 20, the ignited high temperature combustion gases from the injection chamber 10 enter the feed chamber 30 where the combustion gases are mixed with finely divided material containing metallurgical fines injected through inlet 31. Finely divided material injected into the feed chamber 30 is mixed by turbulent flow with the combustion gases from the oxygen and natural gas. The temperature of the mixture in the feed chamber 30 is above 2000° C. The feed chamber is surrounded by a cooling jacket 32, typically of eighth inch or quarter inch wide passageways, through which water is circulated to cool the walls of the feed chamber 30.

From the feed chamber 30, the combustion gases are mixed with the finely divided material and are then moved into the reaction chamber 40. In the reaction chamber 40, with the high temperatures, vapors of metal disassociate from the oxides as the mixture moves downwardly through the reaction chamber 40. The reaction chamber 40 is provided with cooling jacket 42 on the outside, typically of quarter inch or eighth inch wide passageways through which coolant water can be circulated, to cool the walls of the reaction chamber 40. Molten slag is formed in the reaction chamber 40.

From the reaction chamber 40, the mixture of combustion gases and molten particles with metal vapor is moved through transition piece 45 surrounded by cooling jacket 46 to slag separation chamber 50. The slag separation chamber 50 is covered with the cooling jacket 52 typically including eighth inch or quarter inch wide passageways through which coolant water can be circulated, as shown in detail in FIGS. 5 and 7. Circulation of water through the passageways in the cooling jacket cool wall portions of the chamber 40.

The mixture of combustion gases and molten particulate with metal vapor enters slag separation chamber 50 tangentially as shown in FIG. 5, where the centrifugal force causes molten slag to adhere to the cylindrical sides of the slag separation chamber 50. The slag separation chamber is also angled as shown in FIG. 5 to cause the molten slag to form a pool 53 in the slag separation 50. As shown in FIG. 8, tap 54 is provided to allow the molten slag in pool 53 to be taken off from the system either continuously and intermittently to apparatus 56. To keep the slag in a fluid state and to prevent air from entering the slag separation 50, a permanent or temporary heat unit 55 may be provided adjacent to tap 54.

The zinc vapor and other metal vapors from the ignited high temperature combustion gases and finely divided particulate at the slag separation chamber 50 are transported to plenum 60 under negative pressure. Air is drawn through the plenum to oxidize the metal vapor to metal oxide particulates, e.g. zinc oxide. Alternatively, a fan or blower may be used to introduce air through the plenum near the portion adjacent the slag separation. Plenum 60 has an insulated surround 61 and with the negative pressure the airborne particulates and vapor in the transported mix are taken up the plenum 60 as shown in FIG. 2.

At the top of plenum 60, the airborne particulates and vapor are transported to baghouse 70 as shown in FIG. 2. In baghouse 70, the airborne particulate and vapor is circulated and directed by baffles 71, with particulate of zinc oxide and other metal oxides collected with bags 72 in baghouse 70. The remaining air is exhausted to the atmosphere at 73.

Table I below shows carbon monoxide to carbon dioxide ratio (CO/CO₂); zinc recovery to CZO, burner oxygen to natural gas ratio, and distribution head oxygen to natural gas ratio, as projected for the disclosed invention.

TABLE I Zinc Burner Distribution CO/CO₂ Recovery to oxygen-to- Head oxygen- Ratio CZO natural gas to-natural gas 0.318 93.04% 1.99 1.10 0.187 88.05% 1.96 1.17 0.229 87.51% 1.79 0.97 0.397 94.82% 1.85 1.01 0.260 91.53% 2.02 1.07

The exemplary embodiments were chosen and described in order to explain some of the principles of the present invention so that others skilled in the art may practice the invention. While certain embodiments of the present invention are described in detail above, the scope of the invention is not to be considered limited by such disclosure, and modifications are possible without departing from the spirit of the invention as evidenced by the following claims: 

What is claimed is:
 1. A method of recovering zinc oxide and other metal oxides from metallurgical fines, comprising: a. forming in an injection chamber a mixture of natural gas and oxygen and then igniting the mixture to form high temperature combustion gases of greater than 2000° C. with a high concentration of carbon monoxide; b. transporting the ignited high temperature combustion gases through a quiescent chamber surrounded by a cooling jacket and located below the injection chamber; c. transporting the ignited high temperature combustion gases from the quiescent chamber to a feed chamber surrounded by a cooling jacket and located below the quiescent chamber; d. forming in the feed chamber a mixture of the ignited high temperature combustion gases with injected finely divided material including EAF dust; e. transporting the mixture of the ignited high temperature combustion gases with injected finely divided material including EAF dust to a reaction chamber surrounded by a cooling jacket, wherein carbon monoxide in the ignited high temperature combustion gases react with metal compounds in the finely divided material forming zinc vapor and other metal vapors and molten slag particles; f. transporting said mixture, including the zinc vapor and other metal vapors and slag particles, from the reaction chamber through a transition piece to a slag separation chamber surrounded by a cooling jacket and located tangentially to the reaction chamber, wherein the zinc vapor and other metal vapors are separated from the molten slag particles; g. transporting the zinc vapor and other metal vapors to an insulated plenum, wherein the zinc vapor and other metal vapors are mixed with air and become airborne zinc oxide and other metal oxides; and h. transporting the airborne zinc oxide and other metal oxides from the insulated plenum to a filter baghouse where zinc and other metal oxides are collected and remaining gases are released to the atmosphere.
 2. The method of recovering zinc oxides and other metals oxides as claimed in claim 1, wherein components of the injection chamber are made of copper.
 3. The method of recovering zinc oxides and other metals oxides as claimed in claim 1, wherein components of the quiescent chamber are made of copper.
 4. The method of recovering zinc oxides and other metals oxides as claimed in claim 1, wherein components of the feed chamber are made of copper.
 5. The method of recovering zinc oxides and other metals oxides as claimed in claim 1, wherein the quiescent chamber is an extension of the injection chamber.
 6. The method of recovering zinc oxides and other metals oxides as claimed in claim 1, wherein the quiescent chamber is an extension of the feed chamber.
 7. The method of recovering zinc oxides and other metals oxides as claimed in claim 1 further comprising a tap in the slag separation chamber to remove collected slag from the slag separation chamber.
 8. The method of recovering zinc oxides and other metals oxides as claimed in claim 7 further comprising a heating unit provided in the slag separation chamber inhibiting air from entering the slag separation chamber and maintaining slag fluidity.
 9. A apparatus for recovering zinc oxide and other metal oxides from metallurgical fines, comprising: a. an injection chamber, where natural gas and oxygen are mixed and then ignited to form high temperature combustion gases of greater than 2000° C. with a high concentration of carbon monoxide; b. a quiescent chamber surrounded by a cooling jacket, where the ignited high temperature combustion gases are transported to; c. a feed chamber surrounded by a cooling jacket, where the ignited high temperature combustion gases are mixed with finely divided material including EAF dust; d. a reaction chamber surrounded by a cooling jacket, where carbon monoxide in the ignited high temperature combustion gases react with metal compounds in the finely divided material forming zinc vapor and other metal vapors and molten slag particles; e. a slag separation chamber surrounded by a cooling jacket and tangentially to the reaction chamber, where the zinc vapor and other metal vapors are separated from molten slag particles; f. an insulated plenum, where the zinc vapor and other metal vapors are mixed with air and become airborne zinc oxide and other metal oxides; and g. a filter baghouse, where the zinc oxide and other metal oxides are collected and remaining gases are released to the atmosphere.
 10. The apparatus for recovering zinc oxide and other metal oxides as claimed in claim 9, wherein components of the injection chamber are made of copper.
 11. The apparatus of recovering zinc oxides and other metals oxides as claimed in claim 9, wherein components of the quiescent chamber are made of copper.
 12. The apparatus of recovering zinc oxides and other metals oxides as claimed in claim 9, wherein components of the feed chamber are made of copper.
 13. The apparatus of recovering zinc oxides and other metals oxides as claimed in claim 9, wherein the quiescent chamber is an extension of the injection chamber.
 14. The apparatus of recovering zinc oxides and other metals oxides as claimed in claim 9, wherein the quiescent chamber is an extension of the feed chamber.
 15. The apparatus of recovering zinc oxides and other metals oxides as claimed in claim 9 further comprising a tap in the slag separation chamber to remove collected slag from the slag separation chamber.
 16. The apparatus of recovering zinc oxides and other metals oxides as claimed in claim 15 further comprising a heating unit provided in the slag separation chamber inhibiting air from entering the slag separation chamber and maintaining slag fluidity. 